The present invention relates generally to gantry cranes and more particularly relates to a shock absorbing bumper used to absorb contact energy between relatively movable members of a gantry crane.
Gantry cranes are commonly used in shipping or construction applications for lifting, moving, and positioning large and/or heavy objects. For example, a gantry crane may be used in shipping yards for loading and unloading containers and other cargo or loads to and from various transportation vehicles. Such a crane typically includes a steel frame supported on a plurality of wheels for mobility. The frame generally includes two pairs of vertically upright columns with horizontal beams mounted to extend between the upper ends of the columns for rigidity. The frame provides overhead support for various crane components, depending upon the desired application.
For grasping objects to be lifted, the gantry crane is typically equipped with a grappler that is made vertically moveable by a lifting mechanism. Various lifting mechanisms are known in the art. For example, in some cranes, the lifting mechanism includes a wire rope hoist system that movably suspends the grappler from trolleys traversably disposed on the horizontal beams. In other cranes, the lifting mechanism includes stabilizer beams adapted to move vertically with respect to the columns. A trolley is supported by each of the stabilizer beams and can drivably traverse the stabilizer beam in a horizontal direction. The trolleys in turn support the grappler for grasping or otherwise securing the container. In such a crane, loading and unloading maybe accomplished by securing a object with the grappler, vertically lifting the object by raising the stabilizer beams, and laterally moving the grappler by traversing the trolleys along the stabilizer beams before lowering the object into its new position.
To maintain proper alignment of the movable stabilizer beams, each end of each stabilizer beam is guided along a respective one of the columns. In one conventional system, a track is vertically disposed along an inner side of the column, and the end of the adjacent stabilizer beam is equipped with a guide assembly to follow vertically along the track. This allows vertical movement of the stabilizer beam with respect to the column while generally keeping the stabilizer beam aligned to the columns. To account for dimensional variations and structural deflections, a clearance gap is provided between each end of the stabilizer beam and the inner face of the column. The stabilizer beam is capable of limited lateral motion between the columns as limited by the clearance gaps.
When the trolley traverses the stabilizer beam, its horizontal acceleration and deceleration produce transverse (side-to-side) reactionary forces that are transferred to the stabilizer beam. The stabilizer beam can also be subject to such transverse forces from movement of the crane. Because the stabilizer beam is not tightly constrained between the columns, the imparted reactionary forces cause the stabilizer beam to shift laterally across the clearance gap located between the end of the stabilizer beam and the column. In an attempt to avoid impacts and high wear between the stabilizer beam and column, gantry cranes have been equipped with shock absorbing devices positioned within the clearance gaps. More specifically, elastically deformable bumpers have been mounted to the ends of the stabilizer beams to cushion the contact with the columns.
Unfortunately, conventional bumpers can be susceptible to rapid wear and require frequent replacement, resulting in repetitive maintenance costs. Moreover, replacing the bumpers requires that the gantry crane be taken out of active service resulting in additional losses.
The present invention overcomes the deficiencies of the prior art by providing a bumper that resists wear while providing suitable energy absorption between the stabilizer beam and the columns. In particular, the invention provides a wear pad made of a wear resistant material for use in combination with an elastically deformable bumper body. The wear pad is mounted to the bumper body so that the wear pad will receive any direct contact with the column, and the bumper body absorbs energy from an impact between the stabilizer beam and the column. The wear pad is made of a durable material that is more resistant than the bumper body to wear from friction, so the wear pad enhances the life of the bumper while decreasing friction. The wear pad may be provided as an auxiliary device to be mounted to a conventional bumper in a retrofit manner.
In an embodiment, the invention provides a two-piece bumper assembly including the wear pad and the bumper body. The bumper body has a base end adapted for mounting to the stabilizer beam within the transverse gap between the end of the stabilizer beam and the inner face of the column. The wear pad is secured to a distal end of the bumper body and has a generally planar contact surface that faces away from the stabilizer beam and toward the column.
Advantageously, the bumper prevents direct contact in a lateral direction between the stabilizer beam and the column, avoiding a metal-to-metal contact that would result in high wear and high friction. Furthermore, the wear pad is the only element that directly contacts the column, thereby avoiding contact between the column and the bumper body. This enables the bumper body to absorb impact energy without subjecting the bumper body to frictional wear from vertical movement of the stabilizer beam relative to the column. Moreover, the wear resistant wear pad is capable of withstanding prolonged sliding contact with the column, thereby increasing the service life of the bumper and reducing the need for maintenance.
In an embodiment, the bumper assembly is sized smaller than the gap between the stabilizer beam and the column, and accordingly, the wear pad contacts the column only occasionally. Alternatively, the bumper can be sized slightly greater than the gap so that the contact surface of the wear pad is in continuous contact with the column. The latter configuration results in a slight preload on the deformable bumper body.
In an embodiment, the bumper optionally includes an internal lubrication reservoir. More particularly, the bumper body includes an interior cavity with an opening at the distal end of the bumper body and the wear pad includes a passage that extends from the cavity to an opening at the contact surface. When the wear pad is secured to the bumper body, the opening and the passage align to provide fluid communication between the contact surface and the interior cavity. Additionally, a channel is disposed through a side of the bumper body to the interior cavity. A lubricant may be supplied through the channel to the interior cavity, which acts as a reservoir to contain the lubricant. The lubricant is automatically delivered through the passage for application to the contact surface during use.